Impact/Purpose:

Recently, the U.S. EPA added an urban site located in the U.S. Midwest to the Superfund National Priorities List. This site was found to contain Pb-contamination generated by a lead smelter and other industrial lead-related operations. The U.S. EPA also issued a time-critical removal action to address contaminated soils on a number of properties with Pb concentrations ≥400 mg/kg, and in residences with children having elevated blood lead levels within the impacted area. This removal action removed the top 15 cm of the contaminated soil from the residences and replaced it with clean soil to reduce the risk of lead exposure.
The removed soil was stockpiled within the city limits. Later, the city proposed the utilization of this stockpiled soil as a fill to expand an existing city park. To prevent the potential exposure to the lead-contaminated soil, the city proposed that the park would be capped with 30 cm of clean soil. Nonetheless, it was uncertain if the Pb and other contaminants in the stockpiled soil. or in the site itself, would migrate into groundwater. The objectives of this study were to determine if the stockpiled soil was suitable for the intended fill purpose and to predict the environmental risk of elements migrating from the studied soils into groundwater using leaching tests.

Description:

A series of leaching and partitioning tests (Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), Controlled Acidity Leaching Protocol (CALP), Acid Neutralization Capacity (ANC), and sequential extraction) were applied to three different soils to study potential mobility of metals into groundwater. Two of these soils were lead (Pb)-contaminated soils (Hotspot 1 and Hotspot 2) collected from an urban site associated with lead smelting and other industrial operations. The third sample (Stockpile) was soil affected by previous contamination in the area, removed from residential properties, stockpiled, and selected to be used as fill material in the studied site. The TCLP and CALP showed that Pb could be released from both hotspots, but were not released in the acidic rainfall extraction fluid of the SPLP. The sequential extraction showed that Pb in the hotspot soils was associated with the carbonate fraction, while As was associated with the Fe and Mn oxides. The stockpile released traces of Pb or As in the TCLP and CALP, but the ANC only released Pb under acidic conditions and the SPLP did not release Pb or As. Overall, the projected repository with Stockpile would not pose imminent danger to groundwater because, under the expected environmental conditions, Pb and As tend to remain in the solid phase.